Section 4. USB Communications
Description: The value is a byte that represents the devices polling interval for the Interrupt
In Endpoint. The value can be set in the range of 1 – 255 and has units of
milliseconds. The polling interval tells the host how often to poll the device
for card data packets. For example, if the polling interval is set to 10, the host
will poll the device for card data packets every 10ms. This property can be
used to speed up or slow down the time it takes to send card data to the host.
The trade-off is that speeding up the card data transfer rate increases the USB
bus bandwidth used by the device, and slowing down the card data transfer
rate decreases the USB bus bandwidth used by the device. The value of this
property, if any, will be sent to the host when the host requests the device’s
USB endpoint descriptor.
This property is stored in non-volatile memory, so it will persist when the unit
is power cycled. When this property is changed, the unit must be reset (see
Command Number 2) or power cycled to have these changes take effect.
Example Set POLLING INTERVAL property Request (Hex):
Example Set POLLING INTERVAL property Response (Hex):
Example Get POLLING INTERVAL property Request (Hex):
Example Get POLLING INTERVAL property Response (Hex):
MAX PACKET SIZE PROPERTY
Property ID: 0x03
Property Type: Byte
Length: 1 byte
Get Property: Yes
Set Property: Yes
Default Value: 8
Description: The value is a byte that represents the devices maximum packet size for the
Interrupt In Endpoint. The value can be set in the range of 1 – 64 and has
units of bytes. The maximum packet size tells the host the maximum size of
the Interrupt In Endpoint packets. For example, if the maximum packet size is
set to 8, the device will send HID reports in multiple packets of 8 bytes each
or less for the last packet of the report. This property can be used to speed up
or slow down the time it takes to send card data to the host. Larger packet
sizes speed up communications and smaller packet sizes slow down
communications. The trade-off is that speeding up the card data transfer rate
increases the USB bus bandwidth used by the device, and slowing down the
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